1. Field of the Invention
The present invention relates to a method of reassigning addresses and, in particular, to a method of adaptively reassigning addresses of nodes according to changes in volume of a wireless personal area network such as Zigbee network.
2. Description of the Related Art
In recent years, a Personal Area Network (PAN) gains popularity and attention in contrast to a Local Area Network (LAN) or a Wide Area Network (WAN). The PAN allows devices owned by respective persons to form one network for the sake of convenience, which may be implemented in a wireless network field, so that it is referred to as a Wireless PAN (WPAN).
IEEE (Institute of Electrical and Electronics Engineers) 802.15, a Working Group 15, sets the WPAN as a standard of a short range wireless network. The IEEE 802.15 includes four Task Groups (TG) under the WPAN. IEEE 802.15.1, Task Group 1, deals with the famous Bluetooth, IEEE 802.15.2, Task Group 2, deals with coexistence of Wireless LAN (IEEE 802.11) and Wireless PAN, IEEE 802.15.3 and IEEE 802.15.3a, Task Group 3 is in fact two groups: a Group 3 which deals with WPAN High Rate and a Group 3a which deals with WPAN Alternate Higher Rate. In short, both groups deal with high rate WPAN standards (20 Mbit/s or higher), and IEEE 802.15.4, a Task Group 4, also referred to as Zigbee, performs standardization on a low rate WPAN of 250 kbps or less.
In particular, in case of the ZigBee, standardization is conducted on a protocol stack, which operates above the IEEE 802.15.4 PHY/MAC layer for a wireless sensor network by the ZigBee Alliance, which is a federation of companies for building a low power monitoring control system with reliable and cost-effective features.
One of the main functions of the Zigbee network protocol is to allocate logical addresses for building a cluster tree. The cluster tree is formed by setting the ZigBee coordinator as a top level root and connecting all nodes within the ZigBee network as a sub tree structure to the top level root. When the ZigBee network is formed to build the tree, each node is allocated a logical address from its parent node. Such a 16-bit logical address is used within the ZigBee network instead of the old IEEE-64 bit address, to thereby reduce the packet size.
The ZigBee coordinator determines the number of maximum child nodes “Cm” each parent node may have and also determines the number of the maximum levels or depths “Lm” in the tree in order to allocate a logical address to each node when the Zigbee network is formed. Each parent node calculates the block size and Cskip, and receives an allocated logical address block to be used by its child node(s) from the ZigBee coordinator based on the determination of the Cm and Lm values.
After the network is formed by allocating addresses as described-above, the volume of the network may need to be changed by expanding or reducing the size of the network.
For example, when the number of maximum child nodes, which is initially determined, needs to be expanded from four to five or more in response to the change in network volume or when the number of maximum levels needs to be expanded from three to four or more, each address of the nodes allocated from the Zigbee coordinator must be changed when the network is formed.
However, a method of changing the values of Lm and Cm determined by the Zigbee coordinator when the network is formed is not taken into account in the conventional Zigbee network. Accordingly, in order for the Zigbee coordinator to change the values of Lm and Cm after the network is initially formed, all nodes within the Zigbee network must perform a new network join procedure to receive newly allocated logical addresses from the respective parent nodes.
According to this approach, even when each node skips the network discovery procedure to immediately perform the network join procedure, 2(n−1) times of packet transmission is required for a Zigbee network of n nodes, which causes network resources to be wasted. In addition, during the reassignment of addresses in accordance with the above-described procedure, the data packet transmission is not normally performed, which causes network overheads to be increased so that the whole data transmission becomes delayed.
Meanwhile, each node retains in an address mapping table 64-bit IEEE addresses of the other nodes but not its own 64-bit IEEE address and 16-bit logical address information mapped thereto. However, when Lm and Cm are changed, the logical address of each node retained in the address mapping table is changed so that the information of the address mapping table is no longer valid, which requires an additional packet to be exchanged in order to update the information of the address mapping table. Accordingly, additional network resources must be wasted.